[clang-tidy] Add CLANG_TIDY_CONFUSABLE_CHARS_GEN cmake cache variable to avoid building when cross compiling

This is similar to the LLVM_TABLEGEN, CLANG_TABLEGEN and
CLANG_PSEUDO_GEN cmake cache variables.

Differential Revision: https://reviews.llvm.org/D129799

(cherry picked from commit dc95d0c)

Author: mstorsjo

clang-tools-extra/clang-tidy/misc/CMakeLists.txt

@@ -3,7 +3,13 @@ set(LLVM_LINK_COMPONENTS
   Support
   )
 
-if(LLVM_USE_HOST_TOOLS)
+set(CLANG_TIDY_CONFUSABLE_CHARS_GEN "clang-tidy-confusable-chars-gen" CACHE
+  STRING "Host clang-tidy-confusable-chars-gen executable. Saves building if cross-compiling.")
+
+if(NOT CLANG_TIDY_CONFUSABLE_CHARS_GEN STREQUAL "clang-tidy-confusable-chars-gen")
+  set(make_confusable_table ${CLANG_TIDY_CONFUSABLE_CHARS_GEN})
+  set(make_confusable_table_target ${CLANG_TIDY_CONFUSABLE_CHARS_GEN})
+elseif(LLVM_USE_HOST_TOOLS)
   build_native_tool(clang-tidy-confusable-chars-gen make_confusable_table)
   set(make_confusable_table_target "${make_confusable_table}")
 else()